Bile Esculin Medium

Bile Esculin medium is a differential medium in the isolation and presumptive identification of enterococci/group D streptococci. Esculin hydrolysis was first described by Rochaix in 19241 and Swan introduced the use of Bile Esculin Agar in 19542. The ability to hydrolyze esculin in the presence of bile is a characteristic of enterococci and group D streptococci. According to Facklam and Moody the bile esculin test provided a reliable means of identifying group D streptococci and differentiating them from non-group D streptococci3. Other researchers have used this medium for the presumptive identification of Enterobacter spp., Klebsiella spp., and Serratia spp., among the Enterobacteriaceae.

Enterococci and certain streptococci hydrolyze esculin, to esculetin and dextrose. Esculetin then reacts with Ferric citrate froming a dark brown or black iron complex from its original amber color. This color formation is an indicator of esculin hydrolysis. Oxgall is added to the medium for additional selectivity where it inhibits growth of gram-positive bacteria other than enterococci. There are a few streptococci that do not hydrolyze esculin but will grow in the presence of bile. Growth without blackening of this medium does not constitute a positive test.

Product Name Catalog # Quantity
Bile Esculin Agar mono plate, 90 x 15 mm C-BEA-1001 10/pk
Bile Esculin Agar mono plate, 90 x 15 mm C-BEA-1005 50/pk
Bile Esculin Agar mono plate, 90 x 15 mm C-BEA-1010 100/pk
Bile Esculin Agar Slant C-BES-1001 10/pk
Bile Esculin Agar Slant C-BES-1002 20/pk
Bile Esculin Agar Slant C-BES-1002 100/pk
Bile Esculin Broth C-BEB-1001 20/pk

Quality Control

The following organisms are routinely used for testing for this medium.
Test Organisms Results
aEnterococcus faecalisb ATCC® 29212 Growth; blackening of media around colonies
aStreptococcus pyogenes ATCC® 19615 Partial to complete inhibition
aRecommended QC strains for User Quality Control according to the CLSI document M22 when applicable

User Quality Control

Check for signs of contamination and deterioration. Users of commercially prepared media may be required to perform quality control testing with at least one known organism to demonstrate growth or a positive reaction; and at least one organism to demonstrate inhibition or a negative reaction (where applicable).

Ingredients g/L

(Final pH 6.6 +/- 0.2 at 25°C)
Oxbile (Oxgall) 40.0
Pancreatic Digest of Casein 5.0
Beef Extract 3.0
Esculin 1.0
Ferric Citrate 0.5
Agar (where applicable) 15.0

2 total citations

  1. Rochaix. 1924. Cr. Soc. Biol., Paris; 90:771.
  2. Swan, A. 1954. J. Clin. Path.; 7:160-163.
  3. Facklam, R.R., and M.D. Moody. 1970. Appl. Microbiol., 20:245
UFC Biotech Home